Wow, never encountered that one yet.
Highlanders are badass- the gauss rifle is the single most OP weapon in the game- low heat, no recoil pernalties, and can one hit kill with a headshot. But they are rare as ****.
Sadly this one does not come with gauss rifles. That's the SLDF variant from the campaign, hard to find in career mode and I have mechs start empty so even salvaging me one wont get the gauss rifles. (although I doubt I'll encounter them in the field anyway)
The Gauss is nice in that it can do long range head sniping in one hit, but it suffers from the same problems that all the Lostech weapons do. The game's visual range is only 300 meters. This is only one hex outside the range of SRMs, medium lasers, and AC/20s. This means most fights will happen in SRM range. I don't think I've ever been outside range of a Large Laser while having a line of sight on someone, as this would mean my mechs are pretty spread out. So why on earth would I want the extra heat from an ER Large Laser? PPCs are even worse, if I'm outside the range of a PPC that means my spotter is nearly outside sight range of his fire support, and PPCs are already way too hot to be useable anyway, an ER PPC just eliminates my heat budget entirely.
Large Pulse Lasers are a straight downgrade from a PPC, they produce more heat and do less damage at less range. The one benefit is the +2 accuracy bonus, which can be found on a PPC+ anyway or even exceeded on one of the PPC++ models. And the PPCs have stability damage and a sensor debuff on top of it! And comparing LPL to the regular Large Laser, more than double the heat for a 12.5% damage increase. Laughable.
Medium Pulse maaaybe have an argument over the Medium Laser, when hardpoints are in short supply, but in the end the +damage variants overcome all the advantages once again.
AC/10+ makes a good replacement for the Gauss rifle. The +5 or +10 damage variant can also oneshot a head, it weighs 3 tons less, and isn't super rare. If you put those three tons into heatsinks, the net result is actually less heat on the AC/10 than on the Gauss rifle! (also a critical hit to a gauss ammo bin is extremely problematic because you can't just scrounge up more)
In my opinion, the only useful Lostech is the double heat sink, or the mech chassis themselves. I just stole an SLDF Griffon that actually becomes a good battlemech because it simulates an XL engine/endo steel or whatever, they get extra free tonnage. Great for the flashpoints with drop limits. AS7-D-HT Atlas is hands down the best battlemech in the game.
Seventy-eight free tons, 13 more than King Crab or the standard issue Atlas.